Spinnaker sails



Filed. Feb. 7, 1957 Oct. 20,1959 F. E. HOOD? 2,909,142

SP INNAKER SAILS 2 Sheets-Sheet 1 I Oct. 20, 1959 F. EL'HOOD SPINNAKER SAILS 2 Sheets-Sheet 2 Filed Feb. 7, 1957 ewe ESL

' applicable to sailboats.

United States Patent O.

SPINNAKER SAILS Frederick E. Hood, Marblehead, Mass. Application February 7,1957, Serial No. 638,824

8 Claims. (Cl. 114103) depth of spherical curvature when distended by the wind t in position for sailing, and are accordingly too baggy for reaching close to the wind or with the wind abeam or forward of the beam. Thus, they do not have the proper aerodynamic shape for maximum speed at these sailing points. This is especially true as the wind velocity increases, as any increase in wind pressure tends to ex- "aggerate the defects in aerodynamic shape already existing 'in a sail.

It is accordingly a primary object of the present invention to provide a spinnaker sail of improved aerodynamic shape, which is capable of eifectively reaching under greatly varying wind conditions.

' A further object of the invention is to provide a sail Y of the type described which, when distended by the wind,

has a projected area of maximum size within the limits of its girth measurement. sail art the term girth measurement refers to that di- As commonly used in the mension of the sail obtained by measuring its greatest width'along a line parallel-to its bottom edge, which is usually carefully defined and limited by the rating rules Thus, it is an important object ofthe invention to provide a spinnaker sail which during use assumes an unusually flat are along any given horizontal plane with the result that the chord lengths in such planes and the projected area of the sail are considerably greater than is commonly encountered in sails of this .type;

Still further objects and advantages of the invention will be apparent from the following description and appended claims.

I have discovered that it is unnecessary to provide a large degree of curvature in the horizontal planes of a spinnaker sail during use, and that by keeping the degree of horizontal curvature small, a considerable increase in the projected width of the sail for a definite cloth width will take place. I have also discovered that by properly gathering the sail, or by cutting out small portions of the :seamed sections, in the central portion of the sail, chiefly in the upper half thereof. One suitable way of accom- 2,909,1l2 Patented Oct. 20, 1959 ICC plishing this is to provide shortenings along the center vertical seam or seams, in which case the shortenings, and the gatherings thereby formed, are preferably provided almost entirely in the top half of the sail. The objects of the invention can be most eifectively accomplished by providing panels having seamed edges which extend substantially vertically and have curved upper portions whereby the average radius of curvature of the lower portion thereof is at least twice the average radius of curvature in the upper portion of said edges, and by selecting and proportioning the number and size of the gatherings in respect to the size of the sail in such a manner that when the sail is distended by wind pressure from winds with velocities of 5 to 25 m.p.h., the greatest curvature of the average horizontal arc willbe less than a curve with a ratio of chord height to length of 1:4, while at the same time the average vertical arcs of the sail will have at least twice the radius of curvature in the lower half thereof as in the upper half.

When the outer edges of the sail are curved, as shown in the drawings, the most eifective aerodynamic shape of the sail is obtained when gatherings are also provided along these outer vertical edges. In such cases the gatherings of the outer vertical edges are so arranged in size and number that the radius of curvature of the outer 10 to 20% of the horizontal ares is substantially equal to the entire average curvature.

When symmetrically shaped panels are employed the gatherings can be located on both sides of and contiguous with the central vertical seam, and in such case they may be of the same size and symmetrically placed in each panel opposite each other. However, equally good results can be obtained with unsymmetrical panels, where the vertical seam is placed other than centrally of the sail. In such case the gatherings placed farthest from the actual center line of the sail should be the smallest in size. It is also possible to provide one large gathering in one panel and 2 or 3 smaller ones in the other panel. In all instances the gatherings should be positioned for balance, so as to make a smoothly curved sail along horizontal line-s when distended. Although it simplifies formation of the gatherings to provide them along the vertical seam or seams, it is also possible to form them at any desired point preferably in the upper half of the sail regardless of the location or presence of. vertical seams.

A further understanding of the invention will be obtained from the accompanying drawings, in which:

Figure 1 is an isometric view of a sailing yacht carrying a spinnaker and showing the position assumed by the spinnaker when it is distended by the wind and the wind is forward of the beam.

Figure 2 is a plan view of the yacht at line 22 of Figure 1. 1

Figure 3 represents the arc of the sail along line 2-2 of Figure 1.

Figure 4 is a side view of the sail shown in Figure 1.

Figure 5 is a plan view of a pattern suitable for use'in cutting out one of the panels of a typical sail of the invention. I

Figure 6 is a plan view of a panel of the sail made according to the pattern of Figure 5, showing the appearance of the panel before seaming together the various notches cut therein.

Referring to Figure 1, the numeral 10 represents a sailboat reaching with the wind direction forward of the beam, as shown by arrow 12, and carrying the spinnaker 13, which is supported at its upper end 14 by mastlS.

- One lower corner 16 of the sail is fastened to the, free by the curved lines The bottom edge or foot is reprei general, perpendicular to the leaehes 20. Numerals 23a and 23b designate seams formed by seaming together centrally located gatherings or cut-out portions in the sail.

Referring to Figure 2, the top of the said is cut away along the line 22 in Figure 1 to show the shape of the horizontal are 24 and its relation to the boat 10 with the wind direction shown by arrow 12. The curvature of each horizontal are below are 24, as represented approximately by the seams 23, conforms generally with the curvature of are 24 and presents approximately a uniform aerodynamic angle of approach to the wind direction represented by arrow 12.

Figure 3 represents an enlarged view of are 24, which shows how the degree of curvature is limited by limiting the ratio of chord length (c) to chord height (12) at greater than the ratio 4:1. It can be seen that the curve as shown has a generally uniform curvature and definitely does not have a greater curvature or smaller radius near the outer ends as is generally the case with conventional spinnakers, especially under increasing wind pressures. This arc, which also represents the approximate average curvature of all the arcs drawn in horizontal planes through the said, will maintain this approximate shape under the pressure of winds from 5-25 mph, when the sail is made in accordance with this invention and of the usual proper material, such as nylon parachute fabric.

Figure 4 shows the curvature of the sail in Figure 1 in a vertical plane when distended by winds of approximately 5-10 m.p.h. and under the usual sail trimming conditions. A sail made according to this invention will show a vertical curvature in the upper half of line or seam 22, having a radius at least half of that in the lower half of line 22.

A further understanding of the invention will be obtained from the following specific example of a suitable method of making one of the sails of the invention.

A spinnaker sail suitable for a racing cruising boat having its sail area rating determined by the Cruising Club of America rule, and therefore limited to a leach length of 65.3 feet and a maximum width of cloth across the sail of 42.2 feet, was made in the following manner, using a 1.9 ounce nylon rip-stop parachute fabric 40 inches wide made by Duplan Corporation. First, a pattern was marked on the floor of the loft having the configuration shown in Figure 5 and representing the outline of one vertical panel of a typical spinnaker of the inven tion, such as that shown in Figure 1. This was accomplished by first making the base line 25 of the pattern 21.1 feet long, or one-half the length of the foot of the desired sail. Line 26 was then drawn perpendicular to line 25 from point 27 to point 28, a distance of 65.3 feet. Arc 29 having a radius of 15 feet was then drawn from point 28. On this are 36 inches from the intersection of this are and perpendicular 26 a point 30 was located. Fifteen feet from point 30 and also on are 29 point 31 was located. Another are 32 with a radius of 30 feet was then drawn from point 28. On this are 36 inches from the intersection of this are and the perpendicular 26 a point 33 was located. Twenty-one feet from point 33 and also on are 32 point 34 was located. A smooth curve 35 was then drawn from point 28 through points 30 and 33 which then was extended in' almost a straight line from point 33 to point 27. Likewise a smooth curve 36 was drawn from point 28 through points 31 and 34 and extended in almost a straight line to point 37.

After preparing the pattern in the manner above indicated, 14 pieces or strips of cloth 38 of the same width (Figure 6) were cut and laid on the pattern, and made to overlap each other three-quarters of an inch, after which the overlapped portions were stitched to form seams 39 parallel to the bottom edge 40 of the panel thereby formed. The cloth strips were of sufiicient length to extend beyond lines 35 and 36 on the pattern (Figure 5) to allow room for seaming and hemming. On being seamed and hemmed, the end edges of strips 38 formed curved side edges 41 and 42 which were substantially in alignment with lines 35 and 36 of the pattern. A point 43 was then marked on the fourth seam down from head 44'and three feet from edge 41 (Figure 6). A straight line was then drawn on the cloth from point 43 to point 45, which is approximately at the intersection of the third seam down with edge 42. Eighteen inches above point 45 and also on edge 42 point '46 was located. From this point a line was drawn to point 43, after which the segment 454346 was cut out, leaving three-quarters of an inch of cloth for seaming. Point 47 was then marked on the seventh seam down from head 44 and twothirds of the distance from edge 42 to edge 41 of the cloth. Where this seventh seam intersects the line defined by edge 42 point 48 was marked. Point 49 was then marked 34 inches up from point 48 on edge 42, after which the segment 4847-49 was cut out, leaving three-quarters of an inch or cloth for seaming. At every other intersection of the transverse seams 39 with edge 41 V-shaped notches 50 were then cut out having their apexes in line with points 44 and 51 and about one and one-half inches wide at edge 41. When the notches 50 were seamed together, edge 41 of the cloth had a length of 65.3 feet. The notches formed by cutting out segments 45-43-46 and 48-4749 were then seamed, after which a second panel was made in the same manner as described above, and the two panels were combined by sewing together curved edges 42 of each panel. Edge 41 on each panel then formed a leach of the sail, which was then finished in the usual manner by sewing on reinforcements and working eyelets (not shown) at the three corners.

By way of comparison the sail made as hereinbefore described was hoisted on a yacht in place of a conventional spinnaker sail made to the same limiting dimensions. When filled by the wind the sail had a projected area at least 5% greater than that of the conventional spinnaker under the same conditions. Also the sail made in accordance with this invention could be effectively carried at least 5 closer to the wind than the conventional spinnaker.

In practicing this invention on sails of a different size or using other fabrics or materials than that given in the example it will be necessary to vary the amount and proportions of the gatherings somewhat. The amount and spacing of the gatherings in the outer edges of the sail will be correct when the edges show a slight flutter in the wind similar to the ideal leach of a well made mainsail. The placement of the V notches along the center seam will be correct, when there is no apparent ridge formed along this scam, when the sail is distended by the wind. If the center seam, or central portion of the sail, ridges or bulges inwardly it should be lengthened along a vertical line. If it bulges outwardly, it should be shortened.

While the invention has been described with respect to sails comprising two or more panels connected by vertically extending seams, it is also'possible to make sails in the form of a single panel having the desired curvature, as previously defined, and constituting the entire spinnaker. Thus, a sail having the characteristics herein defined can be formed from a single sheet of plastic film, such as cellophane, in which case no seams are required and the proper curvature along both horizontal and vertical lines can be imparted to the sail by properly located gatherings, or cut and seamed portions, or by molding or otherwise shaping the plastic sheet.

One of the advantages of the invention is that it is possible to use a tough elastic fabric, such as nylon with its high ratio of strength to weight and its high tear resistance, without being penalized by the high stretch properties of such fabrics, which ordinarily would allow a spinnaker to go out of shape under variable wind conditions. Other fabrics which may be used in carrying out the invention include fabrics made of fibers such as rayon, including Fortisan fibers made by the Celanese Corporation, silk, and the polyester fiber known as Dacron.

Other modifications and changes in the methods and constructions described herein will be apparent to those skilled in the art without departing from the spirit and intent of this invention. It is to be understood therefore that it is not intended to limit the scope of the invention except as indicated by the scope of the appended claims.

What is claimed is:

1. A spinnaker sail comprising vertically extending panels each having at least one curved side edge extending substantially vertically, said curved side edges being seamed together and said panels being gathered at spaced points along the upper curved portion of said seamed edges, whereby when said sail is distended by the pressure of Wind a smooth and relatively shallow concave form is imparted thereto.

2. A spinnaker sail comprising fabric panels joined together by a substantially vertical seam, said panels and said seam during use of the sail being curved from the vertical in the upper portion thereof, said panels having adjacent the upper portion of said vertical seam a series of seamed notches, whereby said sail in use assumes a smooth and relatively shallow concave form, said sail being further characterized in that the number of seamed notches formed in said panels and the degree of curvature of said vertical seam is sufiicient to produce an average horizontal curvature in the sail, when distended during use, equivalent to that of a curve having a ratio of chord height to chord length of at least one to four.

3. A spinnaker sail comprising at least two fabric panels of substantially triangular configuration, said panels each having at least one curved edge which eX- tends substantially vertically, but curves away from the vertical along its upper portion, said panels being seamed together along said edges and being provided at spaced opposing points along the curved upper portion of said edges with notches of generally V-shape having their apeXes pointing away from said edges, the edges of said notches being seamed together, whereby on distension of said sail during normal use a smooth and relatively shallow concave form is imparted to said sail, the average curvature of the horizontal arcs of the sail during use being that of a curve having a ratio of chord height to chord length of at least one to four, the average radius of curvature of the sail in the vertical plane being at least twice as great in the lower portion of the sail as in the upper portion of the sail.

4. A spinnaker sail substantially as described in claim 3, but further characterized in that the outer vertical edges of the sail are gathered at spaced points and the number of gatherings is selected so that the average radius of curvature of the outer 10 to 20% of the horizontal arcs at each end thereof is substantially equal to the average radius of curvature of the arcs in their entirety.

5. The method of making an improved spinnaker sail which comprises cutting substantially triangular panels of cloth and forming at least one curved edge on said panels, which is curved more sharply as it approaches the apex of said triangular panels, cutting V-shaped notches along the more sharply curved portion of said curved edges, seaming the edges of said notches together, whereby gatherings are formed in the cloth, and then seaming together said panels along said curved edges.

6. The method substantially as described in claim 5, but further characterized in that V-shaped notches are cut in the outside edges of the sail and then the edges of said notches are seamed, a sufficient number of said seamed together notches being formed so that the average radius of curvature of the outer 10 to 20% of the horizontal arcs of the sail is substantially equal to the average radius of the arcs in their entirety.

7. A spinnaker sail comprising vertically extending panels each having at least one curved side edge extending substantially vertically, said curved side edges being seamed together and said panels being provided with gatherings at spaced points in the upper central portion thereof, whereby when said sail is distended by the pres sure of wind a smooth and relatively shallow concave form is imparted thereto.

8. A spinnaker sail of generally elongated shape in a vertical direction which is held at the top and at tWo spaced points at the bottom and having, when distended by the Wind, both curved vertical arcs and curved horizontal arcs, said sail being provided with gatherings at spaced points in the upper central portion thereof, whereby on distention of said sail during normal use a smooth and relatively shallow concave form is imparted to said sail, the average curvature of the horizontal arcs of the sail during use being that of a curve having a ratio of chord height to chord length of at least one to four, the average radius of curvature of the sail in the vertical plane being at least twice as great in the lower portion of the sail as in the upper portion of the sail.

Luders Feb. 10, 1931 Willis Mar. 13, 1951 

